1. Field of the Invention
The present invention relates to wireless identification systems and protocols and more specifically to systems used for detection, identification, control and/or location of events and/or objects.
2. Related Art
Conventional data communication systems have been applied to accomplish object identification using the medium of radio broadcast. Such radio frequency identification (RFID) systems find application in the fields of materials handling, inventory control, and generally in the field of tracking personnel, objects, and animals.
Wireless monitoring systems, such as tag systems, are well known for detecting, locating and/or identifying coded articles. A variety of techniques and systems have been used to determine the identification and/or location of a suitably tagged article. Two basic approaches exist for these tag systems:
The first approach is the use of tags that intermittently or repetitively beacon or broadcast identification, status, or other sensor information without necessarily requiring interaction from other devices. When thousands of beacon type tags are present in a confined environment the intermittent broadcasts often overlap or collide and difficulty is encountered in distinguishing reception of overlapping or colliding broadcasts from multiple tags. In an attempt to overcome this problem, it is known to vary the periods between tag broadcasts, vary the length and type of tag transmissions and other types of variations to provide broadcast diversity in multiple tag environments. This type of intentional variation in tag broadcast is referred to as non-synchronous or Type I transmissions.
A second approach is to use tags that are able to receive transmissions from other devices or sense the occurrence of an event. In this approach, the tags receiving transmissions from other devices may respond to such transmissions by broadcasting information. This approach is analogous to an interrogate and respond system where when information is desired from the tag, a transmission is sent to the tag requesting that it respond with, for example, identification, location, sensor information. When a request for information transmission is broadcast, for example by a reader unit or interrogator, the tags in the area of broadcast respond by transmitting the requested information in their own broadcast. This second type of transmission is referred to as a synchronous or Type II transmission.
These systems are designed for the detection of a single type of event, such as the detection of a merchandise tag entering a designated area and are directed to a particular application having predetermined surveillance area (e.g., adjacent to and exit or loading/unloading point). Conventionally, these systems are typically designed and preset for specific applications and thus different tags and equipment are required for various differences purpose (e.g., beacon type tags verses responding or interrogation type tags). These specific designs represent fixed configurations of systems for utilization with particular applications.
In other applications multiple receivers are positioned at selected points in a surveillance area, for example distributed throughout a warehouse. The receivers are able to identify a location of a tag by for example, the time of receipt, angle of arrival, signal strength and/or phase difference of the transmissions from the transmitting tag or tags.
Conventionally, these systems are confined to single purpose applications. Different tags, readers, protocols and software are required for different system applications. The foregoing systems tend to be relatively complex and expensive because: (i) the number of receivers deployed for surveying an area increases costs of such systems; and (ii) the predefined function of a tag or system requires specific equipment and inventories for each type of application, which also increases associated costs.
Accordingly, it would be beneficial to have monitoring systems and protocols that are flexible depending on the environment in which they are used, wherein such systems and protocols are able to change their utilization automatically, or by programmed instruction to do so.
Moreover, it would be advantageous to have a location detection system where the numbers of complex receiving devices can be reduced.
It would further be advantageous to have monitoring systems that are configured so that tag collisions (i.e., simultaneous receipt of tag transmissions) can be reduced or deciphered and validated more effectively.